As you're talking pig hunting, you're not looking at a suppressed load but rather 125grn class super-sonic ammo. In that case, the 7.62x39 generates over 200fps higher velocities than a 125grn class 300BO load so it's a better choice as a hunting rd for pigs. As you already know, hunting ammo prices are the same for both calibers.
For example, PPU makes excellent brass cased, boxer primed 123grn SP ammo for both calibers at comparable cost on line. In addition, you may already have some Red Army Standard steel cased, berden primed 123grn 7.62x39 fmj ammo (currently available for as little as 19¢ per rd at
Outdoor Unlimited) that works well for practice and plinking.
Nothing wrong with the 300BO, it's just that the 7.62x39 is a faster rd and a fine choice for pigs. So, if you're looking for an excuse to get a RAR in 7.62x39, you've got all the justification you need. Besides, with a second RAR, you can take one of the kids with you pig hunting. Win-Win.